Method of preparing collagen fibers

ABSTRACT

Tannery waste, such as shoulder and belly splits and glue stock, is delimed, pickled in a salt solution containing a strong acid until it loses some of its initial water content and absorbs acid, disintegrated in the presence of excess water whereby it swells to several times it original weight, and then dewatered by contact with a solution of a soluble chloride or sulfate. The partly dewatered material may then be further processed to collagen fibers by tanning and other conventional procedures.

llhited States Patent Krelmr et al.

[151 3,6fi2fl01l 1 Mar. 20, W72

METHOD OF PREPARING COLLAGEN FIBERS Inventors: Milan Kremr; Vaclav Hrabovsky, both of Otrokovice, Czechoslovakia Assignee: Statni vyzkumny ustav Kozedelny, Gottwaldov, Czechoslovakia Filed: Aug. 14, 1969 Appl. No.: 850,236

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References Cited UNITED STATES PATENTS 8/ I929 Serebrianoi ..l62/2 FOREIGN PATENTS OR APPLICATIONS 692,749 8/1964 Canada 162/2 Primary Examiner-Howard R. Caine Attorney-Richard Low [5 7] ABSTRACT 2 Claims, No Drawings METHOD OF PREPARING COLLAGEN FIBERS This invention relates to a method of preparing a collagenous material from tannery wastes.

Synthetic materials have recently begun to replace leather in shoe uppers. While the synthetic materials employed are more readily available than good natural leather, the synthetic materials so far employed are inferior to leather in water vapor permeability and in the ability to conform to the foot of a wearer. Shoe uppers made from collagenous fiber materials are known to be free from these shortcomings of synthetic leather substitutes, but their mechanical properties are inferior.

It has now been found that collagen fibers which have high strength and are free from the brittleness characteristic of the best collagen fibers available heretofore can be obtained from tannery waste, such as split hide and glue stock, when the raw material, while substantially from from lime, is pickled in a liquor of 130-170 percent water, 3-6 percent sodium chloride, and 0.8 to 3.0 percent of a strong inorganic or organic acid whose anion is inert to the collagenous substrate. The percentage figures in this application, unless explicitly stated otherwise, are based on the weight of the tannery waste material, employed as the source of collagen, when containing up to about 70 percent water. The method of the invention results in collagen fibers of high quality, and fibers thus produced may be used, for instance, in the manufacture of high grades of artificial leather and textile products.

When pickling is carried out until equilibrium between the pickled material and the liquor is reached, as indicated by the absence of further pH changes in the pickling liquor, the waste material loses water to the liquor and absorbs acid in such a ratio that its weight is reduced to 95 to 75 percent of the pelt weight. Equilibrium is reached when the pH of the pickling liquor is approximately between 2.6 and 3.6.

The pickled material is then mechanically disintegrated in the presence ofa large excess of water, whereby it is swelled to at least 200 percent of its original weight, and usually to as much as 400 percent. When the swollen mass is contacted with an inorganic salt solution, such as that of a soluble chloride or sulfate of an inert cation, it loses enough water to permit further processing in a conventional manner, for example, the further removal of water by contact with air at ambient or elevated temperature, and division into fibers from which hat felt or upholstery stuffing may be prepared, or which may be bonded to make a material suitable for shoe uppers or converted to fabric, the ultimate processing following conventional methods and not being directly relevant to this invention.

The chemical nature of the acid employed in the important pickling step is not critical. It should be a strong acid which ionizes completely or practically completely at the necessary concentration indicated above. The preferred inorganic acid is sulfuric acid, and the preferred organic acid is formic acid, but other acids of similar strength whose anions are inert to the collagenous material may be substituted at higher cost.

The acid present in the pickled waste material enhances the subsequent swelling of the collagenous material when in contact with water while being disintegrated. The salt content of the pickling liquor must be held at not more than 6 percent because it would otherwise interfere with the swelling of the fibers during disintegration in the presence of water. A minimum of 3 percent sodium chloride in the pickling liquor is essential for proper acid absorption and for the desired shrinkage of the raw material.

Because a shrinking step precedes the swelling and disintegration, only the surface strata of the fibers are fully swollen, thereby permitting easy separation of the fibers without breaking them, while the original, unswollen condition still prevails in the core and protects the fibers against breaking into shorter sections or a shortening of average fiber length.

The disintegrated mass may be homogenized and portions of its water content removed by contact with a solution of a soluble sulfate, chloride, or like inorganic salt which precipitates the collagen molecules of high molecular weight while albumin and other proteinaceous material of smaller molecular weight, if not removed by preceding steps, remain in solution. The careful removal of the lower-weight materials is believed to account for the observed fact that collagen fibers of the invention do not get brittle during drying as is frequently observed with conventionally prepared collagen fibers, and is a prime source of processing difficulties.

Further processing of the collagenous material of the invention follows conventional procedures. The water resistance of the fibers may be improved by tanning, using chromium salts or synthetic tanning agents. As other collagen fibers, the materials of the invention are capable of being treated with cationic or nonionic fat-liquoring agents. Pre-tanning with synthetic tanning agents in amounts of about 5 percent prevents curling ofthe fibers in subsequent chrome tanning.

The tanned fibers of the invention may further be processed in a known manner to make leather substitutes and other products in which collagen fibers have heretofore been employed. In common with known collagen products, the products prepared from the fibers of the invention are permeable to water vapor, yet can be impregnated with water repellants. Good hat felts are readily prepared from the fibers which also are useful as upholstery stuffing material without much further processing.

The following examples further illustrate the invention.

EXAMPLE 1 Cowhide splits, mainly taken from the shoulder and belly parts of the hide and still containing some lime, were received from the tannery. They were washed in running water in a rotating drum for 20 minutes, and the water was then drained from the drum. It was replaced by 200 percent fresh water containing 2 percent ammonium sulfate, and rotation of the drum was resumed for about 3 to 4 hours. All percentage figures relate to the pelt weight of the starting material.

Lime was completely removed from the material by treatment with ammonium sulfate solution which was thereafter drained and washed out with running water for 20 to 30 minutes. As much of the washing water as possible was removed from the drum, and a solution of 4 percent sodium chloride in percent water was rotated with the delimed material for 15 minutes, whereupon 2.5 percent formic acid diluted with five weights of water were added in two batches without stopping rotation of the drum.

The pH of the pickling liquor reached a stable value of 3.2 to 3.4 in about 3 to 4 hours, indicating completion of the pickling process. The pickled hide material was then removed from the drum, permitted to drain for about 1 hour, cut into pieces approximately 4 inches square, and separated into fibers on a disintegrator while suspended in approximately four weights of water which was continuously renewed.

The collagen fibers so obtained were homogenized with water and again precipitated from the homogenized suspension by adding 15 percent sodium chloride. The precipitated material was separated from the supernatant aqueous phase and tanned with a reduced chromium liquor to a Cr O content of 2 percent. Excess water was then removed by passage between squeezing rolls, and the squeezed material was dried at slightly elevated temperature to a water content of approximately 30 percent, whereby it was capable of being carded on an ordinary textile carding machine to produce fibers suitable for felting and other processing as is conventional in the textile industry, when further dried to about 25 percent moisture content.

Closely similar products were obtained from defatted glue stock and other collagenous tannery waste, and the properties of the fibrous material could be modified in a predictable manner by supplementing the chrome tanning process by treatment with synthetic tanning agents and by fat-liquoring with nonionic or cationic agents.

EXAMPLE 2 Cowhide splits were washed, delimed, again washed, and drained as described in Example I. The delimed material was then drummed 15 minutes in a solution of 4 percent sodium chloride in 150 percent water whereupon 1.2 percent sulfuric acid diluted with five weights of water was added to the rotating contents of the drum in two portions at 15 minutes interval. Pickling was continued until the liquor reached a stable pH at 2.8 to 3.0.

The procedure of Example 1 was thereafter followed.

Samples taken from the pickled material of both examples prior to disintegrating were found to have shrunk by water loss, only partly compensated for by acid absorption so that the pickled material weighed only about 80 to 85 percent of the same material prior to pickling. The shrinkage may vary as the amount of acid employed during pickling and other variables are changed within the limits indicated above.

The fibers produced by the method of the invention are stronger and tougher than collagen fibers prepared from the same raw material by conventional methods, more specifically by methods which do not include the treatment with a pickling liquor meeting the composition limits set forth above.

We claim:

1. A method of preparing a collagenous material from waste hide material substantially free from lime, which comprises:

a. pickling said material in a liquor essentially consisting of to percent water, 3 to 6 percent sodium chloride, and 0.8 to 3 percent of a strong acid until the material loses sufficient water to be reduced to 95 to 75 percent of the initial pelt weight thereof, all percentage figures being based on said initial pelt weight;

b. disintegrating the pickled material in the presence of a large excess of water until it swells to at least twice said initial pelt weight;

c. contacting the swollen material with a solution of a soluble sulfate or chloride to separate some of the water thereof from a collagenous remainder; and

d. dividing said partly dewatered remainder into fibers.

2. A method as set forth in claim 1, wherein the amount of said acid is such that equilibrium between said pickled material and said liquor is reached when the pH of said liquor is between 2.6 and 3.6. 

2. A method as set forth in claim 1, wherein the amount of said acid is such that equilibrium between said pickled material and said liquor is reached when the pH of said liquor is between 2.6 and 3.6. 